Self-aligning virtual elliptical drive

ABSTRACT

A self-aligning wobble plate drive, including a stator gear, a wobble plate, and an output plate. The stator gear has a central stator axis and a plurality of stator teeth. The wobble plate has a wobble axis, a plurality of face teeth, and a plurality of wobble teeth, and is disposed such that the wobble axis is at a non-zero wobble angle relative to the stator axis. The output plate includes a plurality of output teeth and is substantially aligned with the stator axis. At least two of the pluralities of teeth are configured to engage with each other in a self-aligning manner such that as the wobble plate nutates around the stator gear, the wobble angle remains constant.

FIELD

This disclosure relates to wobble plate drives. More specifically, thedisclosed embodiments relate to systems and methods for modifying torquewith an elliptically interfacing gear system.

INTRODUCTION

Two or more gears can be used to create a mechanical advantage through agear ratio. There are many ways to arrange gears so that a singlerotation of a first gear results in more or less than one rotation of asecond gear in the same amount of time. In certain applications it isdesirable to have a motor with a very high gear ratio, where the gearreduction takes place in the smallest possible volume.

Historically, wobble plate drive mechanisms have seemed a promisingroute toward a drive having a high gear ratio within a small volume. Ina wobble plate drive, one of the gears, for example a rotor gear,nutates around the other gear, for example a stator gear. As usedherein, the terms “nutate” or “nutation” mean a wobble, a sway, or acircular rocking motion. The rotor gear is typically supported by ashaft or fulcrum that keeps the gear teeth in alignment. If the numberof gear teeth on the rotor gear and the stator gear are different byone, then such a system would have a gear ratio equal to the number ofteeth on the stator gear.

In practice, efficient and effective wobble plate drive systems haveproven to be elusive, because the forces involved often lead todisengagement of the mechanism, binding, over-constraint by the fulcrum,or inefficiency due to friction, among others.

SUMMARY

A self-aligning wobble plate drive includes a stator gear, a wobbleplate, and an output plate. The stator gear has a central stator axisand a plurality of stator teeth disposed on an inner cylindricalsurface. The wobble plate has a wobble axis, an engaging faceperpendicular to the wobble axis, a plurality of face teeth disposed onthe engaging face, and a plurality of wobble teeth disposed around aperimeter of the wobble plate and configured to engage with the statorteeth. The output plate includes a plurality of output teeth configuredto engage with the face teeth.

The wobble plate is disposed such that the wobble axis is at a non-zerowobble angle relative to the stator axis, and the output plate issubstantially aligned with the stator axis. At least two of thepluralities of teeth are configured to engage with each other in aself-aligning manner such that as the wobble plate nutates around thestator gear, the wobble angle remains constant.

A method for operating a self-aligning wobble plate drive includesproviding a stator gear, a wobble plate, and an output plate. The methodfurther includes engaging a plurality of stator teeth of the stator gearwith a plurality of wobble teeth of the wobble plate in a self-aligningmanner. The method then includes engaging a plurality of face teeth ofthe wobble plate with a plurality of output teeth of the output plate ina self-aligning manner. Finally, the method includes inducing nutationof the wobble plate about the stator gear.

The present disclosure provides various apparatuses and methods of usethereof. In some embodiments, a wobble plate drive may include an inputplate, a wobble plate, and a stator. In some embodiments, a drive mayinclude a motor, a wobble plate, a stator, and an output plate. In someembodiments, each of the wobble plate, the stator gear, and the inputplate or output plate may include a set of teeth configured to engagewith each other in a self-aligning manner.

Features, functions, and advantages may be achieved independently invarious embodiments of the present disclosure, or may be combined in yetother embodiments, further details of which can be seen with referenceto the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded isometric view of an exemplary wobble plate drive,according to aspects of the present disclosure.

FIG. 2 is a magnified bottom plan view of a portion of an input plate ofthe wobble plate drive of FIG. 1.

FIG. 3 is a magnified top plan view of a portion of a stator gear of thewobble plate drive of FIG. 1.

FIG. 4 is an exploded isometric front view of another exemplary wobbleplate drive, according to aspects of the present disclosure.

FIG. 5 is an exploded isometric rear view of the wobble plate drive ofFIG. 4.

FIG. 6 is an isometric view of a wobble plate drive of the wobble platedrive of FIG. 4.

FIG. 7 is a cross-sectional view of the wobble plate drive of FIG. 4,taken along a plane parallel to a rotation axis of the drive.

FIG. 8 is another cross-sectional view of the wobble plate drive of FIG.4, taken along a plane rotated 45 degrees from the plane of FIG. 7.

FIG. 9 is a schematic representation of an isometric view of a wobbleplate and a motor, according to aspects of the present disclosure.

FIG. 10 is a diagrammatic representation of an isometric exploded viewof the motor of FIG. 9.

FIG. 11 is a flow chart depicting an exemplary method of use of a wobbleplate drive, according to aspects of the present disclosure.

FIG. 12 is a flow chart depicting another exemplary method of use of awobble plate drive, according to aspects of the present disclosure.

OVERVIEW

Various embodiments of a self-aligning wobble plate drive having awobble plate and a stator are described below and illustrated in theassociated drawings. Unless otherwise specified, a wobble plate driveand/or its various components may, but are not required to, contain atleast one of the structure, components, functionality, and/or variationsdescribed, illustrated, and/or incorporated herein. Furthermore, thestructures, components, functionalities, and/or variations described,illustrated, and/or incorporated herein in connection with the presentteachings may, but are not required to, be included in other wobbleplate drives. The following description of various embodiments is merelyexemplary in nature and is in no way intended to limit the disclosure,its application, or uses. Additionally, the advantages provided by theembodiments, as described below, are illustrative in nature and not allembodiments provide the same advantages or the same degree ofadvantages.

EXAMPLES, COMPONENTS, AND ALTERNATIVES

The following sections describe selected aspects of exemplary wobbleplate drives as well as related systems and/or methods. The examples inthese sections are intended for illustration and should not beinterpreted as limiting the entire scope of the present disclosure. Eachsection may include one or more distinct inventions, and/or contextualor related information, function, and/or structure.

Example 1

An embodiment of a self-aligning virtual elliptical drive, or wobbleplate drive, can be seen in FIG. 1, generally indicated at 10. Drive 10includes an input plate 12, a wobble plate 14, and a stator gear 16.Input plate 12, which may also be referred to an output plate dependingon the intended use of the wobble plate drive, defines a rotation axis20 about which stator gear 16 is centered. Wobble plate 14 has a wobbleaxis 22 disposed at a non-zero angle relative to the rotation axis,which may be referred to as a wobble angle.

Wobble plate 14 has a lower, substantially flat face 24 and an upperengaging face 26 with a plurality of face teeth 28. Face teeth 28 aredisposed on front face 26, and a plurality of wobble teeth 30 aredisposed around a perimeter of the wobble plate between faces 24 and 26,in a plane perpendicular to the wobble axis. The wobble teeth extendparallel to the wobble axis and from face 26 toward face 24.

Wobble plate 14 is disposed between input plate 12 and stator 16. Lowerface 24 is perpendicular to the wobble axis and faces generally towardstator 16, while engaging face 26 defines a plane parallel to the lowerface but faces generally toward input plate 12. Wobble teeth 30 and faceteeth 28 extend in opposite directions parallel to wobble axis 22.

Input plate 12 includes an annular input surface 36 at an outer portionof the input plate, as best seen in FIG. 2. Input surface 36 may befrustoconical. That is, annular input surface 36 is angled relative to aplane perpendicular to the rotation axis 20, so that every point on theannular input surface includes a frustoconical line 38 that can beextended to a vertex located on the rotation axis and below input plate12. When the above-recited elements are assembled into a wobble platedrive, the frustoconical vertex of annular input surface 36 is proximatea center of mass of wobble plate 14.

A plurality or set of input teeth 34 is disposed on annular inputsurface 36. Any appropriate number of input teeth 34 may be used. Eachinput tooth 34 includes two driving faces 40, 42 and each driving facemay be planar, composed of more than one plane, or may be composed ofone or more surfaces with curvature.

As depicted in FIG. 1, front face 26 of wobble plate 14 includes anannular wobble surface 64 at an outer portion of the front face, similarto annular input surface 36 shown in FIG. 2. In other words, annularwobble surface 64 is angled relative to a plane perpendicular to wobbleaxis 22, so that every point on the annular wobble surface includes afrustoconical line that can be extended to a frustoconical vertexlocated on the wobble axis. The frustoconical vertex of annular wobblesurface 64 coincides with a center of mass of wobble plate 14. In otherembodiments, the wobble surface may have a different shape.

A plurality or set of face teeth 28 is disposed on annular wobblesurface 64. Any suitable number of face teeth 28 may be chosen, and thenumber of face teeth may be more, less, or the same as the number ofinput teeth 34. In the depicted embodiment, there are equal numbers offace teeth 28 and input teeth 34. Each face tooth includes two drivenfaces, which may be planar, composed of more than one plane, or may becomposed of one or more surfaces with curvature.

Wobble plate 14 is configured to engage with input plate 12. Morespecifically, face teeth 28 are configured to engage with input teeth34. When the input plate rotates in a given rotation direction a drivingface of an input tooth may engage with a driven face of a face tooth.That is, there may be a contact force exerted on the wobble plate by theinput plate through an interaction between the driving faces of theplurality of input teeth and the driven faces of the plurality of faceteeth. These contact forces may cause the wobble plate to rotate in thesame given rotation direction.

In the example of drive 10, input plate 12 and wobble plate 14 interactand rotate according to a gear ratio of 1:1. That is, for every singlecomplete rotation of the input plate, the wobble plate also completesexactly one complete rotation. Other choices for the gear ratio arepossible, and would result in differing rates of rotation.

Wobble plate 14 and input plate 12 may be configured so that any contactforces exerted between the wobble plate and the input plate will pointin directions that are tangent to circles which lie in planesperpendicular to the rotation axis. By configuring the wobble plate andinput plate so that contact forces between the wobble plate and theinput plate point in such directions, eccentric forces may be avoided.Eccentric forces may cause the plurality of face teeth 28 to disengagefrom the plurality of input teeth 34 or may cause the center of mass ofthe wobble plate to oscillate, thereby introducing undesirablevibrations into the drive.

The complementary shapes of frustoconical input surface 36 and wobblesurface 64 cause input teeth 34 and face teeth 28 to engage at an anglesuch that if drive 10 experiences vibration or displacement, contactforces between the teeth urge input plate 12 and wobble plate 14 backinto alignment. Input teeth 34 and face teeth 28 therefore engage in aself-aligning manner, such that the wobble angle remains constant as theinput plate and wobble plate rotate.

As shown in FIG. 1, stator gear 16 has a base 48, and the base includesan inner cylindrical surface 50 and a stator tooth base 52. Base 48 mayinclude attachment points configured to operatively couple stator 16 tothe rest of a device using drive 10 (for example, a device within whichdrive 10 is incorporated). Stator 16 may be stationary relative to thatdevice. The stator gear defines a stator axis 54 that is substantiallyaligned with rotation axis 20.

Stator 16 has an interior volume 56 partially defined by innercylindrical surface 50. Interior volume 56 may be configured toaccommodate some or all of wobble plate 14, as described in more detailbelow.

Stator teeth 32 may be disposed on either or both of inner cylindricalsurface 50 and stator tooth base 52. In the embodiment of FIG. 1, thestator teeth extend from the inner cylindrical surface into interiorvolume 56 in a radial direction toward the rotation axis. The statorteeth also extend from stator tooth base 52 in an axial directionparallel the rotation axis. Any suitable number of stator teeth may bechosen, depending on the application and desired gear ratio.

FIG. 3 is a top plan view of stator gear 16, showing a subset of theplurality of stator teeth 32. Each tooth of the plurality of statorteeth has a proximal end and a distal end, relative to rotation axis 20.The distal end of a stator tooth may be coupled to inner cylindricalsurface 50. Each tooth also includes a first engaging surface 66 and onthe opposite side of the tooth, a second engaging surface 68. Eachengaging surface may be planar, composed of more than one plane, orcomposed of one or more surfaces with curvature. One or both engagingsurfaces 66, 68 of a stator tooth 32 may be defined by a compoundinvolute of a circle and an ellipse. Alternately, the curve may be theprojection of a virtual ellipse onto the tooth location for all anglesbetween 0 and 2π radians.

Each of the plurality of stator teeth 32 is wedge-shaped. That is, thefirst engaging surface 66 defines a line 70 that is extendable throughthe rotation axis. Line 70 passes through the center of mass of thewobble plate when both the wobble plate and the stator gear are coupledtogether within the drive. The second engaging surface 68 defines a line72 that is also extendable through the wobble axis. Line 72 also passesthrough the center of mass of the wobble plate when both the wobbleplate and the stator gear are coupled together within the gearboxsystem.

Each tooth of the plurality of stator teeth 32 includes an engagingportion and a supporting base. The engaging portion includes the firstengaging surface and the second engaging surface. The supporting basecouples the engaging portion to stator tooth base 52. The stator teethmay also be supported by other structures, or coupled to the statortooth base in any appropriate manner.

As shown in FIG. 1, the plurality of wobble teeth 30 are disposed arounda perimeter of wobble plate 14 between lower face 24 and engaging face26 and in a plane perpendicular to wobble axis 22. The wobble teethextend from an outer cylindrical surface 58 of the wobble plate in aradial direction away from the wobble axis. The wobble teeth also extendfrom a wobble tooth base 60 in an axial direction along the wobble axis.The wobble tooth base may be an approximately annular member coupled toor integral with the wobble plate. Connecting the wobble teeth to eitheror both of the cylindrical surface or the wobble tooth base may lendphysical support or a degree of rigidity to the plurality of wobbleteeth. Any suitable number of wobble teeth 30 may be chosen, and thenumber of wobble teeth may be more, less, or the same as the number ofstator teeth 32.

Similarly to stator teeth 32 shown in FIG. 3, each wobble tooth 30includes a first engaging surface and on the opposite side of the tooth,a second engaging surface. Each surface may be planar, composed of morethan one plane, or composed of one or more surfaces with curvature. Oneor both engaging surfaces of a wobble tooth 30 may be defined by acompound involute of a circle and an ellipse. Alternately, the curve maybe the projection of a virtual ellipse onto the tooth location for allangles between 0 and 2π radians.

Each of the plurality of wobble teeth is wedge shaped. That is, thefirst engaging surface defines a first line that is extendable throughthe wobble axis. The second engaging surface defines a second line thatis extendable through the wobble axis. The first and second lines bothpass through the center of mass of the wobble plate.

Additionally, each wobble tooth 30 includes an engaging portion and asupporting base. The engaging portion includes the first engagingsurface and the second engaging surface. The supporting base connectsthe engaging portion to wobble tooth base 60. The wobble teeth may alsobe supported by other structures, or coupled to the wobble tooth base inany other appropriate manner

Wobble plate 14 is configured to engage with stator gear 16. Morespecifically, wobble teeth 30 are configured to engage with stator teeth32. In the case where input plate 12 rotates in a first rotationdirection, the first engaging surface of a wobble tooth may engage withthe first engaging surface of a stator tooth. That is, there may be acontact force exerted on the wobble plate by the stator gear through aninteraction between the first engaging surfaces of the plurality ofstator teeth and the first engaging surfaces of the first plurality ofwobble teeth. These contact forces may cause the wobble plate to rotatein the first rotation direction and nutate in a first nutationdirection.

In general, the stator gear has n stator teeth and the wobble plate hasm wobble teeth, where n and m are integers that differ by one or more,but typically by one. As the wobble plate nutates around the statorgear, each tooth in the plurality of wobble teeth may engage with onetooth in the plurality of stator teeth during a single nutation. Asthere may be one more stator teeth than wobble teeth, the wobble platemay rotate slightly during a single nutation.

Specifically, the wobble plate may rotate 1/m of a complete rotationduring a single nutation of the wobble plate. In other words, if thewobble plate rotates by 1/m of a complete rotation, perhaps due to aninteraction with the input plate, the wobble plate may complete one fullnutation. Thus, the wobble plate and the stator gear may interactaccording to a gear ratio of m:1. For every m nutations of the wobbleplate, the wobble plate may rotate exactly once. Thus, the gear ratio ofthe disclosed systems can be determined by the number of teeth m and nof the wobble plate and stator gear, respectively.

The wobble plate and the stator gear may be configured so that anycontact forces exerted between them will point in directions that aretangent to circles which lie in planes perpendicular to the rotationaxis. Contact forces may point in a direction that is substantiallyperpendicular to the wobble axis 22 and to a radial line extending froma point of contact between a wobble tooth 30 and a stator tooth 32 tothe wobble axis 22.

The wedge shapes of stator teeth 32 and wobble teeth 30 definecomplementary conical surfaces and cause the teeth to engage at an anglesuch that if drive 10 experiences vibration or displacement, contactforces resulting from engagement urge wobble plate 14 back intoalignment with stator gear 16. The teeth therefore engage in aself-aligning manner, such that the wobble angle remains constant as thewobble plate nutates about the stator.

Wobble plate 14 and stator gear 16 are substantially circular in shape,with a projection of the wobble plate onto the stator being ellipticaldue to their differing orientations. The pluralities of wobble teeth 30and stator teeth 32 may be contoured by projecting this virtual ellipseonto the tooth location. The elliptical projection of wobble plate 14onto stator 16 may thereby be constrained to non-eccentric rotation.Eccentric motion, if allowed, may drive large imbalance forces creatingunacceptable system performance.

The wobble plate drive may be understood as a mechanically constrainedsystem governed by Euler's equations for a wobbling plate, which createa rotating inertial reference frame. Consider Euler's z-axis equation,T _(z) =I _(z){dot over (ω)}_(z)−(I _(x) −I _(y))ω_(x)ω_(y)

where T is torque, I is moment of inertia, and ω is angular velocity.This equation shows that depending on the direction of torque, an axiswill experience an opposing rotation. Torque, or kinetic energy, mayenter the system and be accepted as opposing rotations. Input energy maybe used in changing a momentum vector of wobble plate 14.

Wobble teeth 30 and stator teeth 32 may be configured to provide amechanical constraint on motion of wobble plate 14, for example theengaging surfaces of the teeth may be defined by a compound involute ofa circle and an ellipse. In such a configuration, the maximum possiblerotational velocity of the wobble plate is less than or equal to thevelocity needed to satisfy the solution to Euler's equations. As thewobble plate is subjected to acceleration, this results in a forceacting to increase the wobble angle. The force is balanced by contactwith input plate 12, keeping the wobble angle constant.

In other words, when the nutating wobble plate undergoes torque byengagement with the input plate, the wobble angle will tend to increase.The input plate is spaced from the stator at a predetermined distancesuch that it constrains the wobble plate relative to the stator gear.The wobble angle therefore remains constant and no part of the wobbleplate is more than the predetermined distance from the stator gear asthe wobble plate nutates around the stator.

The exemplary wobble plate drives described in the present teachings mayeither store and absorb input torque, or may output a limited amount ofstored torque. In the first case, input teeth 34 of input plate 12engage face teeth 28 of wobble plate 14 to cause the plate to rotate.Wobble teeth 30 of the wobble plate engage stator teeth 32 of statorgear 16 to induce nutation of the wobble plate. The wobble plate storesand absorbs the input torque as nutation.

The wobble plate drive may be considered in terms of the virtual ellipseformed by projecting the wobble plate onto the stator. Wobble plate 14and stator 16 may have generally one point of contact. An edge of thevirtual ellipse may define in three dimensions a continuous line ofcontact of the elliptically interfacing wobble plate and stator. Theshape of the virtual ellipse may remain unchanged under a nutation ofthe wobble plate that encompasses four times the angle between thewobble axis 22 and rotation axis 20. Only the rotational frame of theline of contact, defined by Euler's equations, may advance as thenutation occurs. Each point on the line of contact may fall on acompound geometrically distorted involute function, and the function maybe symmetric under both rotation and nutation, allowing continuousenergy transfer to and from the virtual ellipse.

The virtual ellipse may be static as the inertial frame rotates, withall points on the line of contact rotating in their own horizontal planeat a constant angular rate. A point on a radial edge of wobble plate 14viewed during nutation may exhibit vertical motion with a constantlychanging velocity. This change in velocity may require constantacceleration of the inertia of the wobble plate, absorbing kineticenergy input to the system.

In the second case, where the wobble plate drive outputs stored torque,rotation of the wobble plate may cause the input plate to rotate. Inthis case, wobble plate 14 is rotating and nutating, but input plate 12does not experience external torque.

When the wobble plate rotates in a first direction, the first drivenface of a wobble tooth may engage with the first driving face of aninput tooth. That is, there may be a contact force exerted on the inputplate by the wobble plate through an interaction between the firstdriven faces of the plurality of face teeth and the first driving facesof the plurality of input teeth. These contact forces may cause theinput plate to rotate in the first direction. In other words, the inputplate may be considered an output plate.

Example 2

Another embodiment of a self-aligning virtual elliptical drive can beseen from different angles in FIGS. 4 and 5, and is generally indicatedat 110. Drive 110 includes an input motor 112, a wobble plate 114, astator gear 116, and an output plate 118. Motor 112 defines a rotationaxis 120, about which stator gear 116 and output plate 118 are centered.Wobble plate 114 is disposed at a non-zero angle relative to therotation axis.

Wobble plate 114 has a rear, substantially flat face 124 and a frontface 126 with a plurality of face teeth 128 and a plurality of wobbleteeth 130. Face teeth 128 are disposed on front face 126, and wobbleteeth 130 are disposed around a perimeter of the wobble plate betweenfaces 124 and 126, in a plane perpendicular to the wobble axis. Wobbleteeth 130 and face teeth 128 extend in the same direction parallel towobble axis 122 (shown in FIG. 6).

When drive 110 is assembled, motor 112 engages with rear face 124 ofwobble plate 114 to induce the wobble plate to nutate about stator 116.The stator, which also may be referred to as a stator gear, includes aplurality of stator teeth 132 configured to engage with wobble teeth130, and thereby induce the wobble plate to rotate. Output plate 118includes a plurality of output teeth 134 configured to engage with faceteeth 128, and the wobble plate thereby induces the output plate torotate also. In this manner motor 112 may rotate output plate 118 with atorque determined by a first gear ratio between wobble plate 114 andstator 116, and a second gear ratio between wobble plate 114 and outputplate 118.

In the embodiment pictured in FIGS. 4 and 5, input motor 112 is anelectric motor with a substantially flat surface 136 perpendicular torotation axis 120 and including a first cartridge bearing 138 and asecond cartridge bearing 140 coupled to the flat surface. Bearings 138,140 may be best seen in FIG. 4. The first bearing may be angularlyspaced from the second bearing by 89 degrees, as measured with respectto axis of rotation 120. The bearings may be coupled to flat surface 136proximate a radial edge of the surface.

Bearings 138, 140 extend from surface 136 such that either bearing 138or bearing 140 is in contact with rear face 124 of the wobble plate.This contact is at a point angularly spaced by 45 degrees, as measuredwith respect to the axis of rotation, from a point of closest approachbetween the motor and the wobble plate. The bearings are configured tomake rolling contact with rear face 124 of wobble plate 114, and therebyengage with the wobble plate to induce nutation.

In other embodiments, not pictured, a single rounded protrusion (ratherthan two protrusions) may be formed on flat surface 136 of motor 112.The rounded protrusion may make contact with wobble plate 114 at a pointangularly spaced from the point of closest approach by 45 degrees, asmeasured with respect to the axis of rotation. Other embodiments mayinclude two protrusions spaced apart by an angle between 80 and 100degrees, but not necessarily exactly 89 degrees. Still other embodimentsmay include three or more projections extending from flat surface 136.

Regardless of the number of rounded protrusions, a lubricant may bedisposed between motor 112 and wobble plate 114, to reduce frictionbetween the rounded protrusions and rear face 124 of the wobble plate.Furthermore, the protrusions may take any shape, or include anymechanism tending to provide low friction rolling engagement of theprotrusion(s) with wobble plate 114.

As shown in FIG. 6, wobble plate 114 is shaped similarly to a disc, witha rear face 124, a front face 126 and a central axis, or wobble axis122. Wobble plate 114 is aligned such that wobble axis 122 forms anon-zero angle with axis of rotation 120. Rear face 124 is perpendicularto the axis of rotation, while front face 126 defines a plane parallelto the rear face. As shown in FIGS. 4-5, rear face 124 faces generallytoward input motor 112 and front face 126 faces generally away from themotor.

Returning to FIGS. 4-5, the plurality of wobble teeth 130 are disposedaround a perimeter of wobble plate 114 between rear face 124 and frontface 126 and in a plane perpendicular to wobble axis 122. The wobbleteeth extend from an outer cylindrical surface 158 of the wobble platein a radial direction away from the wobble axis. The wobble teeth alsoextend from a wobble tooth base 160 in an axial direction along thewobble axis. The wobble tooth base may be an approximately annularmember coupled to or integral with the wobble plate. The plurality ofwobble teeth may extend from both cylindrical surface 158 and wobbletooth base 160. Connecting the wobble teeth to either or both of thecylindrical surface or the wobble tooth base may lend physical supportor a degree of rigidity to the plurality of wobble teeth. Any suitablenumber of wobble teeth 130 may be chosen.

Each wobble tooth 130 includes a first engaging surface and on theopposite side of the tooth, a second engaging surface. Each surface maybe planar, composed of more than one plane, or composed of one or moresurfaces with curvature. One or both engaging surfaces of a wobble tooth130 may be defined by a compound involute of a circle and an ellipse, aswill be discussed in more detail below. Alternately, the curve may bethe projection of a virtual ellipse onto the tooth location for allangles between 0 and 2π radians.

Additionally, each wobble tooth 130 includes an engaging portion and asupporting base. The engaging portion includes the first engagingsurface and the second engaging surface. The supporting base connectsthe engaging portion to wobble tooth base 160.

For each tooth of the plurality of wobble teeth 130 and stator teeth132, one or both of the first engaging surface and second engagingsurface may be defined by a compound involute of a circle and anellipse. That is, the curve of the second engaging surface may bedefined by a first equation:y=C(tan(φ)−φ)^(D)  eq. (1)where C is a constant which may be proportional to a radius of thewobble plate, φ may take values from 0 to

$\frac{\pi}{2}$radians, and D may have be a positive constant less than 1. D may have avalue of approximately 0.65, though other values are also possible.Equation (1) above may be normalized to unity.

Alternately, the curve of the second engaging surface may be defined bya second equation:y=C(sin(φ)−φ cos(φ))^(D)  eq. (2)where C is a constant which may be proportional to a radius of thewobble plate, φ may take values from 0 to

$\frac{\pi}{2}$radians, and D may have be a positive constant less than 1. D may have avalue of approximately 0.65, though other values are also possible.

Equation (2) above may be normalized to a radius of the wobble plate.The curve of the second engaging surface may be the projection of avirtual ellipse onto the tooth location for all angles between 0 and 2πradians. The curve of the first engaging surface may be a mirror imageof the curve of the second engaging surface, reflected across a planethrough the apex of the tooth and containing the axis of rotation. Also,the first engaging surface and the second engaging surface may meetsmoothly at the apex of each tooth. The cross-sectional shape of thetooth may therefore be defined by a compound involute of a circle and anellipse.

As depicted in FIG. 6, front face 126 of wobble plate 114 includes anannular wobble surface 164, which in the depicted embodiment is afrustoconical surface. That is, annular wobble surface 164 is angledrelative to a plane perpendicular to wobble axis 122, so that everypoint on the annular wobble surface includes a frustoconical line thatcan be extended to a frustoconical vertex located on the wobble axis.The frustoconical vertex of annular wobble surface 164 coincides with acenter of mass of wobble plate 114. In other embodiments, the wobblesurface may have a different shape.

A plurality or set of face teeth 128 is disposed on annular wobblesurface 164. Any suitable number of face teeth 128 may be chosen, andthe number of face teeth may be more, less, or the same as the number ofoutput teeth 134. In the depicted embodiment, there are equal numbers offace teeth 128 and output teeth 134. Each face tooth includes twodriving faces, which may be planar, composed of more than one plane, ormay be composed of one or more surfaces with curvature.

Referring again to FIGS. 4-5, stator gear 116 has a base 148 and thebase includes an inner cylindrical surface 150 and a stator tooth base152. Base 148 may include attachment points configured to operativelycouple stator 116 to the rest of whatever device is using drive 110.Stator 116 may be stationary within the context of that device. Thestator gear defines a stator axis 154 that is substantially aligned withrotation axis 120, and therefore also with the output axis. The statoris disposed between wobble plate 114 and output plate 118.

Stator 116 has an interior volume 156 which is partially defined byinner cylindrical surface 150. Interior volume 156 may be configured toaccommodate some or all of wobble plate 114 as described in more detailbelow.

Stator teeth 132 may be disposed on either or both of inner cylindricalsurface 150 and stator tooth base 152. The stator teeth extend from theinner cylindrical surface into interior volume 156 in a radial directiontoward the rotation axis. The stator teeth also extend from stator toothbase 152 in an axial direction along the rotation axis. Any suitablenumber of stator teeth may be chosen, depending on the application anddesired gear ratio. The number of stator teeth may be more, less, or thesame as the number of wobble teeth 130.

Each tooth of the plurality of stator teeth may have a proximal end anda distal end, relative to rotation axis 120. The distal end of a statortooth may be coupled to inner cylindrical surface 150. Each toothincludes a first engaging surface and on the opposite side of the tooth,a second engaging surface. Each engaging surface may be planar, composedof more than one plane, or composed of one or more surfaces withcurvature.

One or both engaging surfaces of a stator tooth 132 may be defined by acompound involute of a circle and an ellipse, as previously described.Alternately, the curve may be the projection of a virtual ellipse ontothe tooth location for all angles between 0 and 2π radians.

Each tooth of the plurality of stator teeth 132 includes an engagingportion and a supporting base. The engaging portion includes the firstengaging surface and the second engaging surface. The supporting basecouples the engaging portion to stator tooth base 152.

As depicted in FIGS. 4-5, output plate 118 includes a plurality ofoutput teeth 134 disposed on an annular output surface 162. Output plate118 also has an output axis substantially aligned with rotation axis120.

Best seen in FIG. 5, output surface 162 is frustoconical. That is,annular output surface 162 is angled relative to a plane perpendicularto the rotation axis 120, so that every point on the annular outputsurface includes a frustoconical line that can be extended to afrustoconical vertex located on the rotation axis and forward of outputplate 118. When the above-recited elements are assembled into drive 110,the frustoconical vertex of annular output surface 162 coincides with acenter of mass of wobble plate 114. In other embodiments, the outputsurface may have different shapes, such as cylindrical or frustoconicalwith a different vertex.

Any suitable number of output teeth 134 may be chosen, and the number ofoutput teeth may be more, less, or the same as the number of face teeth128. Each output tooth may include two driven faces and each driven facemay be planar, composed of more than one plane, or may be composed ofone or more surfaces with curvature.

FIGS. 7-8 are cross-sectional views of drive 110, showing motor 112,wobble plate 114, stator gear 116, and output plate 118 in an assembledconfiguration. The motor and output plate are aligned along stator axis154. That is, the rotation axis, the output axis, and the stator axisare substantially aligned. The wobble plate and wobble axis 122 may bedisposed at any desired and suitable non-zero angle relative to thestator axis. As wobble plate 114 nutates around stator 116 and outputplate 118, the center of mass of the wobble plate is substantiallystationary.

FIG. 8 is a cross-section in a plane rotated 45 degrees from the planeof the cross-section of FIG. 7, about stator axis 154, and the angle ineach has been exaggerated to more clearly show relationships betweencomponents.

Wobble plate 114 is configured to engage with stator gear 116. Morespecifically, wobble teeth 130 are configured to engage with statorteeth 132. In the case where motor 112 rotates in a first rotationdirection, the first engaging surface of a wobble tooth may engage withthe first engaging surface of a stator tooth. That is, there may be acontact force exerted on the wobble plate by the stator gear through aninteraction between the first engaging surfaces of the plurality ofstator teeth and the first engaging surfaces of the first plurality ofwobble teeth. These contact forces may cause the wobble plate to rotatein the first rotation direction and nutate in a first nutationdirection.

In general, the stator gear has n stator teeth and the wobble plate hasm wobble teeth, where n and m are integers that differ by one or more,but typically by one. As the wobble plate nutates around the statorgear, each tooth in the plurality of wobble teeth may engage with onetooth in the plurality of stator teeth during a single nutation. Asthere may be one more stator teeth than wobble teeth, the wobble platemay rotate slightly during a single nutation.

Specifically, the wobble plate may rotate 1/m of a complete rotationduring a single nutation of the wobble plate. In other words, if thewobble plate rotates by 1/m of a complete rotation, perhaps due to aninteraction with the motor, the wobble plate may complete one fullnutation. Thus, the wobble plate and the stator gear may interactaccording to a gear ratio of m:1. For every m nutations of the wobbleplate, the wobble plate may rotate exactly once. Thus, the gear ratio ofthe disclosed systems can be determined by the number of teeth m and nof the wobble plate and stator gear, respectively.

The wobble plate and the stator gear may be configured so that anycontact forces exerted between them will point in directions that aretangent to circles which lie in planes perpendicular to the rotationaxis. Contact forces may point in a direction that is substantiallyperpendicular to the wobble axis 122 and to a radial line extending froma point of contact between a wobble tooth 130 and a stator tooth 132 tothe wobble axis 122.

Wobble plate 114 and stator gear 116 are substantially circular inshape, with a projection of the wobble plate onto the stator beingelliptical in shape due to their differing orientations. The pluralitiesof wobble teeth 130 and stator teeth 132 may be contoured by projectingthis virtual ellipse onto the tooth location. The elliptical projectionof wobble plate 114 onto stator 116 may thereby be constrained tonon-eccentric rotation. Eccentric motion, if allowed, may drive largeimbalance forces creating unacceptable system performance.

Wobble plate 114 is also configured to engage with output plate 118,through engagement of face teeth 128 and output teeth 134. When thewobble plate rotates in a first rotation direction, the first drivingface of a wobble tooth may engage with the first driven face of anoutput tooth. That is, there may be a contact force exerted on theoutput plate by the wobble plate through an interaction between thefirst driving faces of the plurality of face teeth and the first drivenfaces of the plurality of output teeth. These contact forces may causethe output plate to rotate in the first rotation direction. When thewobble plate rotates in a second rotation direction, contact forcesbetween the second driving faces of the wobble teeth and the seconddriven faces of the output teeth may cause the output plate to rotate inthe second rotation direction.

In exemplary wobble plate drive 110, the output plate and the wobbleplate have the same number of teeth, i.e., the number of output teeth isequal to the number of face teeth. Accordingly, in the depictedembodiment, the output plate and the wobble plate interact and rotateaccording to a gear ratio of 1:1. That is, for every complete rotationof the wobble plate, the output plate also completes exactly onecomplete rotation. Other choices for the numbers of output and faceteeth are possible and would lead to other values for the output gearratio.

Wobble plate 114 and output plate 118 may be configured so that anycontact forces exerted between them will point in directions that aretangent to circles which lie in planes perpendicular to the rotationaxis. For example, a contact force may point in a direction that issubstantially perpendicular to the wobble axis 122 and to radial lineextending from a point of contact between a face tooth 128 and an outputtooth 134 to the wobble axis 122.

By configuring the wobble plate and output plate so that contact forcesbetween them point in such directions, eccentric forces may be avoided.Eccentric forces may cause the plurality of face teeth to disengage fromthe plurality of output teeth or may cause the center of mass of thewobble plate to oscillate, thereby introducing undesirable vibrationsinto the drive system.

Wobble plate 114 may have a 0-degree position or point 142 which may bethe position or point on the wobble plate which is farthest from outputplate 118, as measured in a direction parallel to rotation axis 120. Atthe 0-degree position, shown in FIG. 7, the wobble plate 114 may beclosest to motor 112. Wobble plate 114 may have a 90-degree position orpoint which may be one-fourth of the way around the wobble plate fromthe 0-degree position in a first nutation direction. For example, asviewed from a vantage point above the wobble plate near the outputplate, the 90-degree position may be ninety degrees around a perimeterof the wobble plate in a counter-clockwise direction. Continuing aroundthe perimeter of the wobble plate, a 180-degree position or point 144may be located on the opposite side of the wobble plate as the 0-degreeposition 142. The 180-degree position may mark the closest approach ofthe wobble plate to the output plate and the stator gear and the pointof farthest distance from the motor. A 270-degree position or point maybe located on the opposite side of the wobble plate as the 90-degreeposition.

Motor 112 may be disposed such that 0-degree point 142 is in contactwith flat surface 136 of the motor between bearings 138, 140 (not shown)at a given instant of time, as depicted in FIG. 7. At that same instantof time, only one of bearings 138, 140 may be in contact with rear face124 of wobble plate 114 at a point 146, as depicted in FIG. 8. The motormay be configured to rotate the bearings around stator axis 154 andthereby cause wobble plate 114 to nutate around stator gear 116, withwobble axis 122 precessing around the stator axis. The point of contact146 between the bearing and wobble plate 114 may therefore move ahead of180-degree point 144.

In a case where the motor rotates in a first direction, bearing 138 maybe in contact with rear face 124 of the wobble plate at a point between0-degree position 142 and the 270-degree position and may engage withthe wobble plate to cause the wobble plate to nutate in a firstdirection. FIG. 8 shows bearing 138 in such a case. In a case where themotor rotates in a second direction, bearing 140 may be in contact withrear face 124 of the wobble plate at a point between 0-degree position142 and the 90-degree position and may engage with the wobble plate tocause the wobble plate to nutate in a second direction.

When drive 110 is in use, wobble plate 114 will generally nutate andalso rotate. The wobble plate may be described as configured to nutatearound stator gear 116, around motor 112, and/or around output plate118. In the case where the wobble plate is nutating in the firstnutation direction, the 0-degree position of the wobble plate may movetoward a current location of the 90-degree position so that, after onequarter of a full nutation, the 90-degree position has become the0-degree position, the 180-degree position has become the 90-degreeposition, etc. Furthermore, the wobble plate may not rotate at the samerate it nutates. That is, as the wobble plate completes a single fullnutation, the 0-degree position may travel the full perimeter of thewobble plate. During this same time, the wobble plate may rotate lessthan one full rotation. The rate of rotation may be determined by therate of nutation and by the gear ratio between wobble teeth 130 andstator gear 116.

Wobble teeth 130 may engage with stator teeth 132 along one-fourth ofthe stator gear at any moment as the wobble plate nutates. Thisengagement may be in the form of a rolling contact, where the firstengaging surfaces roll along one another. This rolling contact may be incontrast to many standard gear interfaces where opposing faces of gearteeth interact via a sliding contact. In general, assuming the same twosurfaces are involved, rolling contact has much less friction thansliding contact between the two surfaces.

The wobble teeth 130 may only make contact with the stator teeth 132between the 0-degree position and the 270-degree position when nutatingin the first nutation direction, and this contact may be limited torolling contact between subsets of the pluralities of wobble and thestator teeth. Thus, the wobble plate may nutate around the stator withless friction than in the case of a sliding contact. Such aconfiguration may lead to an efficient transfer of nutational motion orenergy to rotational motion or energy.

Similarly, face teeth 128 may only engage with output teeth 134 alongone-fourth of the output plate at any moment as the wobble platenutates. When the wobble plate nutates in the first direction, the faceteeth and output teeth may engage between 180-degree position 144 andthe 90 degree position. By this engagement, wobble plate 114 may causeoutput plate 118 to rotate in the same direction as the wobble plate. Inthe pictured embodiment, where the gear ratio between face teeth 128 andoutput teeth 134 is 1, output plate 118 may also rotate at the same rateas wobble plate 114. Rotation of motor 112 thus may be transferred tooutput plate 118 at a higher torque.

Example 3

FIG. 9 is a schematic representation of a motor 212 and a wobble plate214 of another embodiment of a self-aligning virtual elliptical drive,generally indicated at 210. The embodiment of FIG. 9 may be similar towobble plate drive 110 described in Example 2, and the discussion ofvarious features and benefits of drive 110 will not be repeated in itsentirety with regard to drive 210. Similar components may be numberedsimilarly, but incremented by 200.

Wobble plate 214 has a wobble axis 222, a substantially flat rear face,a front face with a plurality of face teeth, and a plurality of wobbleteeth disposed around a perimeter of the wobble plate between the flatface and the front face. The face teeth and wobble teeth are notindicated in FIG. 9, but may be as shown in FIG. 6, for example. Thewobble plate drive further includes an output plate with output teethand a stator with stator teeth, not pictured, but which may be aspreviously described in Example 2 (see FIGS. 4-5).

Motor 212 has a motor axis 220. The wobble plate is configured to nutatearound the motor, with the wobble axis precessing around the motor axis.That is, the wobble plate 214 has a mobile point of closest approach 242with respect to the motor. The mobile point of closest approach 242 maymove in a direction of nutation, indicated by arrow 243, around themotor axis 220.

In exemplary drive 210, nutation of the wobble plate 214 around themotor 212 is driven by electromagnetic forces applied to the wobbleplate. These forces originate from the motor and are applied to thewobble plate at a location that is ahead of mobile point of closestapproach 242 in the direction of nutation 243.

A force, indicated by arrow 245 in FIG. 9, is applied to the wobbleplate 214 at a leading point 246, 90 degrees from mobile point ofclosest approach 242. Force 245 is an attractive force and may pointtoward the motor 212 or along a direction parallel to the motor axis220. As the wobble plate nutates and the 0-degree position 242 and theleading point 246 both move around the wobble plate, force 245 alsomoves around the wobble plate so that force 245 is always applied to thewobble plate proximate leading point 246. That is, the applied force 245may be said to be ahead of the mobile point of closest approach in thedirection of nutation 243. The applied force ahead of the mobile pointof closest approach of the wobble plate causes nutation of the wobbleplate.

Force 245 is a result of a response of the material of wobble plate 214to electromagnetic fields created by motor 212. The motor includes apermanent magnet and a set of electromagnetic coils. The permanentmagnet and the set of electromagnetic coils are collectively configuredto create a magnetic field between the motor and the wobble plate. Thatis, a magnetic field is created in a gap 266 between the motor 212 andthe wobble plate 214. The wobble plate is made of a magneticallysusceptible material configured to respond to the magnetic field.Magnetically susceptible materials may become magnetized themselves inthe presence of a magnetic field. The wobble plate responds byexperiencing a force such as force 245.

Forces applied to the wobble plate may be proportional to the fluxdensity of the magnetic field between the wobble plate and the motor. Toaffect an applied force at a mobile location ahead of mobile point ofclosest approach 242, the permanent magnet and the set ofelectromagnetic coils may be configured to create a magnetic field witha highest flux density at a mobile location ahead of the mobile point ofclosest approach in the nutation direction 243. The electromagneticcoils may be configured so that the highest flux density of magneticfield remains ahead of the mobile point of closest approach as thewobble plate nutates.

FIG. 10 is a diagrammatic representation of an isometric exploded viewof motor 212. The motor includes a permanent magnet 268, a motor core270, a set of magnetically susceptible pole pieces 272, and a set ofelectromagnetic coils 274. Relative dispositions and orientations ofcomponents of motor 212 may be described relative to the motor axis. Theterm “axially” will refer to linear directions which are parallel tomotor axis 220. The term “radially” will refer to linear directionswhich are perpendicular to the motor axis 220. The term“circumferentially” will refer to angular directions around, but notalong or away from, the motor axis.

Permanent magnet 268 may have any appropriate shape and may beconfigured to generate any appropriate magnetic field. In the picturedexample, the permanent magnet is cylindrical, with the motor axis 220 asa symmetry axis, and includes a passage 276 through the permanent magnetalong the motor axis. Permanent magnet 268 may be constructed of anyappropriate ferromagnetic material. Permanent magnet 268 has north andsouth magnetic poles substantially aligned along the motor axis 220. Themagnetic field created by the permanent magnet may be referred to as aprimary magnetic field.

Motor core 270 is disposed below the permanent magnet 268. Motor core270 may be formed of a magnetically susceptible material capable ofacquiring a magnetic moment when placed in a magnetic field. Forexample, motor core 270 may be made of electrical steel or iron. Motorcore 270 may have any appropriate shape. In the pictured example, themotor core is cylindrical, with the motor axis 220 as a symmetry axisand a radius matching a radius of the permanent magnet 268. The motorcore includes a passage 278 aligned with passage 276 through thepermanent magnet.

Motor 212 includes a horizontal spacer 280 disposed between thepermanent magnet 268 and the motor core 270. Horizontal spacer 280 maylimit the magnetic field transferred from the permanent magnet to themotor core and may help regulate the magnitude of the magnetic fieldcreated by motor 212.

The set of magnetically susceptible pole pieces 272 are distributedcircumferentially around the motor core 270. The pole pieces 272 maydirect magnetic fields within motor 212 from one component of the motorto another. The pole pieces may be made of any suitable magneticallysusceptible material, such as electrical steel. There may be anyappropriate number of pole pieces. The embodiment shown in FIG. 10includes twelve pole pieces. The pole pieces may have any appropriateshape. The twelve pole pieces shown in FIG. 10 are wedge-shaped and mayalternately be described as wedge pieces. The pole pieces 272 areseparated by a set of vertical spacers 282, which help to isolatemagnetic fields in the pole pieces between the vertical spacers.

The set of magnetically susceptible pole pieces 272 collectively have anupper surface area 284. The pole pieces may be sized and configured sothat the magnitude of the upper surface area is a predetermined multipleof an upper surface area of the permanent magnet 268. In someembodiments, the upper surface area 284 of the pole pieces may be threetimes the upper surface area of the permanent magnet.

The set of electromagnetic coils 274 are disposed circumferentiallyaround the motor core 270 and between the motor core and themagnetically susceptible pole pieces 272. The set of electromagneticcoils includes a first set of electromagnetic coils and a second set ofelectromagnetic coils. In the pictured example, the first set ofelectromagnetic coils includes three inner electromagnetic coils 286 andthe second set of electromagnetic coils includes three outerelectromagnetic coils 288. The three outer electromagnetic coils 288 aredisposed between the inner electromagnetic coils 286 and the set ofmagnetically susceptible pole pieces 272. The first and second sets ofelectromagnetic coils may include any appropriate number of coils,including two, three, and more than three coils. The numbers of coils inthe first and second sets of electromagnetic coils need not be the same.

Each of the first set of electromagnetic coils 286 overlapscircumferentially with each of an adjacent pair of electromagnetic coilsof the second set of electromagnetic coils 288. Each of the second setof electromagnetic coils 288 overlaps circumferentially with each of anadjacent pair of electromagnetic coils of the first set ofelectromagnetic coils 286. Each of the set of electromagnetic coils 274has a coil axis 290 oriented perpendicularly to the motor axis 220. Eachelectromagnetic coil includes one or more conductors forming a pluralityof closed loops around the coil axis 290. When each of the set ofelectromagnetic coils carries an electrical current, each coil creates amagnetic field within the coil oriented substantially parallel to thecoil axis.

If inner and outer electromagnetic coils 286 and 288 overlapcircumferentially as described above, magnetic field lines created byone of the electromagnetic coils may pass through one or more closedloops defined by another of the electromagnetic coils. Portions of themagnetic field created by one of the inner electromagnetic coils 286 maypass through each of an adjacent pair of outer electromagnetic coils288. If there is an angular gap 292 between the adjacent pair of outerelectromagnetic coils, then a portion of the magnetic field created bythe inner electromagnetic coil may not pass through either of theadjacent pair of outer electromagnetic coils.

Similarly, portions of the magnetic field created by one of the outerelectromagnetic coils 288 may pass through each of an adjacent pair ofinner electromagnetic coils 286. If there is an angular gap 294 betweenthe adjacent pair of inner electromagnetic coils, then a portion of themagnetic field created by the outer electromagnetic coil may not passthrough either of the adjacent pair of inner electromagnetic coils.

Motor 212 includes an upper member 296 disposed over the permanentmagnet and the set of magnetically susceptible pole pieces 272. Theupper member may cover the upper surface area of the pole pieces and theupper surface area of the permanent magnet. The upper member includes apassage 298 substantially aligned with the passage 276 through thepermanent magnet. Upper member 296 may be made of any appropriatematerial, such as magnetically susceptible material such as electricalsteel.

The magnetic field created by the motor enters and exits the uppermember in an axial direction. Wobble plate 214 is disposed with thesubstantially flat rear face proximate upper member 296 with a gapbetween the motor and the wobble plate. Magnetic field lines exit themotor through the upper member in a substantially axial direction,traverse the gap between the motor and the wobble plate, travel throughthe wobble plate, again traverse the gap between the wobble plate andthe motor, and enter the motor through the upper member in asubstantially axial direction.

When motor 212 induces wobble plate to nutate the wobble teeth of wobbleplate 214 and stator teeth of the stator may engage to cause the wobbleplate to rotate. The face teeth of wobble plate 214 and output teeth ofthe output plate may engage to cause the output plate to rotate in thesame direction as the wobble plate. Electromagnetic energy of motor 212may thus be converted to rotation of the output plate.

Manner of Operation/Use

FIG. 11 depicts a method, generally indicated at 300, for operating aself-aligning virtual elliptical drive. At step 302, method 300 includesproviding an input plate with input teeth, providing a wobble plate withwobble teeth and face teeth, and providing a stator gear with statorteeth. The input plate, wobble plate, and stator gear may be constructedand assembled as shown, for example, in FIG. 1 and described above inexample 1, or in any other suitable manner and configuration consistentwith the present teachings.

At step 304, method 300 includes rotating the input plate about arotation axis. At step 306, method 300 includes engaging the input teethwith the face teeth, thereby causing the wobble plate to rotate. Theinput teeth and the face teeth may be disposed on frustoconical surfacesforming two complementary cones, such that engagement of the teethcauses the complementary cones to return to alignment. At step 308,method 300 includes engaging the wobble teeth with the stator teeth,thereby causing the wobble plate to nutate. The wobble teeth and thestator teeth may be wedge shaped, the teeth forming two complementarycones, such that the engagement of the teeth causes the complementarycones to return to alignment.

The input plate may be spaced from the stator at a predetermineddistance in order to constrain the wobble plate relative to the statorgear, such that the wobble angle remains constant and no part of thewobble plate can be more than the predetermined distance from the statorgear.

In some embodiments, the method may include dissipating rotationalenergy by nutating the wobble plate. In other embodiments, the methodmay further include stopping rotation of the input plate, and thenallowing inertial energy of the nutating and rotating wobble plate torotate the input plate.

FIG. 12 depicts another method, generally indicated at 400, foroperating a self-aligning virtual elliptical drive. At step 402, method400 includes providing a motor which may include at least one roundedprotrusion on a substantially flat surface and may define a rotationaxis, providing a wobble plate with wobble teeth and face teeth,providing a stator gear with stator teeth, and providing an output platewith output teeth. The motor, wobble plate, stator gear and output platemay be constructed and assembled as shown, for example, in FIGS. 4-8 anddescribed above in example 2, or in any other suitable manner andconfiguration consistent with the present teachings.

At step 404, method 400 includes energizing the motor, which may rotateabout the rotation axis. At step 406, method 400 includes engaging themotor with the wobble plate. The engagement may consist of engaging oneor more of the rounded protrusions of the motor with a substantiallyflat surface of the wobble plate, thereby causing the wobble plate tonutate. At step 408, method 400 includes engaging the wobble teeth withthe stator teeth, thereby causing the wobble plate to rotate. At step410, method 400 includes engaging the face teeth of the wobble platewith the output teeth of the output plate, thereby causing the outputplate to rotate.

The input teeth and the face teeth may be disposed on frustoconicalsurfaces forming two complementary cones, such that engagement of theteeth causes the complementary cones to return to alignment. The wobbleteeth and the stator teeth may be wedge shaped, the teeth forming twocomplementary cones, such that the engagement of the teeth causes thecomplementary cones to return to alignment.

In some embodiments, the method may further include stopping rotation ofthe motor and allowing the output plate to come to a stop. The methodmay further include energizing the motor to rotate in a second rotationdirection about the rotation axis, thereby rotating the output plate ina second direction.

Method 400 may also be used for operating a self-aligning virtualelliptical drive consistent with the configuration described in example3. At step 402, for example, method 400 may include providing a motorhaving a permanent magnet and a set of electromagnetic coils defining acentral axis, providing a wobble plate of a magnetically susceptiblematerial with wobble teeth and face teeth, providing a stator gear withstator teeth, and providing an output plate with output teeth. Themotor, wobble plate, stator gear and output plate may be constructed andassembled as described above in example 3, or in any other suitablemanner and configuration consistent with the present teachings.

When method 400 is used in conjunction with magnetic forces, then atstep 404, method 400 may include energizing the motor, which creates amagnetic field between the motor and the wobble plate with a highestflux density at a mobile location. At step 406, method 400 in this caseincludes engaging the motor with the wobble plate by magnetizing themagnetically susceptible material of the wobble plate with the magneticfield of the motor and thereby applying a force on the wobble plate. Theforce may be applied at the mobile location of highest flux density,leading a point of closest approach between the wobble plate and themotor, and causing the wobble plate to nutate.

At step 408, method 400 includes engaging the wobble teeth with thestator teeth, thereby causing the wobble plate to rotate. At step 410,method 400 includes engaging the face teeth of the wobble plate with theoutput teeth of the output plate, thereby causing the output plate torotate. In some embodiments, the method may further include stoppingrotation of the motor and allowing the output plate to come to a stop.When used in conjunction with magnetic forces, the method may furtherinclude energizing the motor to move the mobile location of highest fluxdensity in an opposite direction, thereby rotating the output plate in asecond direction.

Methods of use according to the present teachings may be employed inconjunction with any of the mechanical virtual elliptical driveembodiments previously described. Although various steps of methods 300and 400 have been described and are depicted in FIGS. 11-12, the stepsneed not necessarily all be performed, in some cases may be performed ina different order than the order shown, and in some cases may beperformed simultaneously.

ADDITIONAL EXAMPLES

This section describes additional aspects and features of examples,presented without limitation as a series of paragraphs, some or all ofwhich may be alphanumerically designated for clarity and efficiency.Each of these paragraphs can be combined with one or more otherparagraphs, and/or with disclosure from elsewhere in this application inany suitable manner. Some of the paragraphs below expressly refer to andfurther limit other paragraphs, providing without limitation examples ofsome of the suitable combinations.

-   A. A wobble plate drive, comprising:-   a stator gear having a central stator axis and a plurality of stator    teeth disposed on an inner cylindrical surface;-   a wobble plate having a wobble axis disposed at a non-zero wobble    angle relative to the stator axis, an engaging face perpendicular to    the wobble axis, a plurality of face teeth disposed on the engaging    face, and a plurality of wobble teeth disposed around a perimeter of    the wobble plate and configured to engage with the stator teeth; and-   an output plate substantially aligned with the stator axis and    having a plurality of output teeth configured to engage with the    face teeth;-   wherein at least two of the pluralities of teeth are configured to    engage with each other in a self-aligning manner such that as the    wobble plate nutates around the stator gear, the wobble angle    remains constant.-   A1. The wobble plate drive of paragraph A, wherein:-   at least one of the wobble teeth is wedge shaped, with a surface of    the at least one wobble tooth defining a first line extendable    through a center of mass of the wobble plate; and-   at least one of the stator teeth is wedge shaped, with a surface of    the at least one stator tooth defining a second line extendable    through a center of mass of the wobble plate.-   A2. The wobble plate drive of paragraph A, wherein:-   The face teeth are disposed on a frustoconical surface of the wobble    plate such that a center of mass of the wobble plate coincides with    a vertex of the frustoconical surface of the wobble plate; and-   the output teeth are disposed on a frustoconical surface of the    output plate such that the center of mass of the wobble plate    coincides with a vertex of the frustoconical surface of the output    plate.-   A3. The wobble plate drive of paragraph A, wherein the wobble plate    is constrained such that during nutation no part of the wobble plate    is more than a predetermined distance from the stator gear.-   A4. The wobble plate drive of paragraph A, wherein the wobble teeth    and the face teeth extend in opposite directions parallel to the    wobble axis, and the wobble plate is disposed between the stator    gear and the output plate.-   A5. The wobble plate drive of paragraph A, wherein the wobble teeth    and the face teeth extend in the same direction parallel to the    wobble axis, and the stator gear is disposed between the wobble    plate and the output plate.-   A6. The wobble plate drive of paragraph A5, further comprising a    motor configured to induce nutation of the wobble plate about the    stator gear, wherein nutation of the wobble plate about the stator    gear causes the wobble plate to rotate, and rotation of the wobble    plate causes the output plate to rotate.-   A7. The wobble plate drive of paragraph A6, wherein:-   the motor is an electric motor having a substantially flat surface    and at least one round protrusion extending from the substantially    flat surface;-   the wobble plate has a substantially flat face opposite the engaging    face; and-   the at least one round protrusion is configured to engage with the    substantially flat face of the wobble plate.-   A8. The wobble plate drive of paragraph A6, wherein:-   the motor includes a permanent magnet and a set of electromagnetic    coils;-   the wobble plate is made of a magnetically susceptible material; and-   the permanent magnet and the set of electromagnetic coils are    collectively configured to create a magnetic field between the motor    and the wobble plate with a highest flux density at a mobile    location.-   B. A wobble plate drive, comprising:-   a stator gear having a central stator axis and a plurality of stator    teeth disposed on an inner cylindrical surface;-   a wobble plate having a wobble axis disposed at a non-zero wobble    angle relative to the stator axis, an engaging face perpendicular to    the wobble axis, a plurality of face teeth disposed on the engaging    face, and a plurality of wobble teeth disposed around a perimeter of    the wobble plate in a plane perpendicular to both the engaging face    and the wobble axis; and-   an output plate substantially aligned with the stator axis and    having a plurality of output teeth configured to engage with the    face teeth; and-   means for self-aligning engagement of the stator teeth with the    wobble teeth, such that the wobble angle remains constant as the    wobble plate nutates around the stator gear.-   B1. The wobble plate drive of paragraph B, wherein:-   at least one of the wobble teeth is wedge shaped, with a surface of    the at least one wobble tooth defining a first line extendable    through a center of mass of the wobble plate; and-   at least one of the stator teeth is wedge shaped, with a surface of    the at least one stator tooth defining a second line extendable    through a center of mass of the wobble plate.-   B2. The wobble plate drive of paragraph B, wherein:-   the face teeth are disposed on a frustoconical surface of the wobble    plate such that a center of mass of the wobble plate coincides with    a vertex of the frustoconical surface of the wobble plate; and-   the output teeth are disposed on a frustoconical surface of the    output plate such that the center of mass of the wobble plate    coincides with a vertex of the frustoconical surface of the output    plate.-   B3. The wobble plate drive of paragraph B, wherein the wobble plate    is constrained such that during nutation no part of the wobble plate    is more than a predetermined distance from the stator gear.-   B4. The wobble plate drive of paragraph B, wherein the wobble teeth    and the face teeth extend in opposite directions parallel to the    wobble axis, and the wobble plate is disposed between the stator    gear and the output plate.-   B5. The wobble plate drive of paragraph B, wherein the wobble teeth    and the face teeth extend in the same direction parallel to the    wobble axis, and the stator gear is disposed between the wobble    plate and the output plate.-   C. A method of operating a wobble plate drive, comprising:-   providing a stator gear, a wobble plate, and an output plate;-   engaging a plurality of stator teeth of the stator gear with a    plurality of wobble teeth of the wobble plate in a self-aligning    manner;-   engaging a plurality of face teeth of the wobble plate with a    plurality of output teeth of the output plate in a self-aligning    manner; and-   inducing nutation of the wobble plate about the stator gear.-   C1. The method of paragraph C, wherein inducing nutation of the    wobble plate includes:-   energizing a motor to rotate about a rotation axis, the motor having    a substantially flat surface and at least one rounded protrusion    extending from the substantially flat surface; and-   engaging the at least one rounded protrusion with a substantially    flat surface of the wobble plate, thereby causing the wobble plate    to nutate.-   C2. The method of paragraph C, wherein inducing nutation of the    wobble plate includes:-   energizing a motor including a permanent magnet and a set of    electromagnetic coils to create a magnetic field between the motor    and the wobble plate with a highest flux density at a mobile    location, thereby causing the wobble plate to nutate.-   C3. The method of paragraph C, wherein:-   inducing nutation of the wobble plate includes rotating the output    plate;-   rotating the output plate when the face teeth are engaged with the    output teeth causes the wobble plate to rotate; and-   rotation of the wobble plate when the stator teeth are engaged with    the wobble teeth causes the wobble plate to nutate.-   C4. The method of paragraph C, further including constraining the    wobble plate such that during nutation no part of the wobble plate    is more than a predetermined distance from the stator gear.

ADVANTAGES, FEATURES, BENEFITS

The different embodiments of a self-aligning wobble plate drivedescribed herein provide several advantages over known solutions fordesigning compact and cost effective wobble plate drives. For example,the illustrative embodiments of a self-aligning wobble plate drivedescribed herein allow a drive without a supporting shaft or fulcrum.Additionally, and among other benefits, illustrative embodiments of theself-aligning wobble plate described herein reduce vibration, heatproduced by friction, and binding of gear teeth. No known system ordevice can perform these functions, particularly in such a small volume.However, not all embodiments described herein provide the sameadvantages or the same degree of advantage.

CONCLUSION

The disclosure set forth above may encompass multiple distinctinventions with independent utility. Although each of these inventionshas been disclosed in its preferred form(s), the specific embodimentsthereof as disclosed and illustrated herein are not to be considered ina limiting sense, because numerous variations are possible. To theextent that section headings are used within this disclosure, suchheadings are for organizational purposes only, and do not constitute acharacterization of any claimed invention. The subject matter of theinvention(s) includes all novel and nonobvious combinations andsubcombinations of the various elements, features, functions, and/orproperties disclosed herein. The following claims particularly point outcertain combinations and subcombinations regarded as novel andnonobvious. Invention(s) embodied in other combinations andsubcombinations of features, functions, elements, and/or properties maybe claimed in applications claiming priority from this or a relatedapplication. Such claims, whether directed to a different invention orto the same invention, and whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the invention(s) of the present disclosure.

We claim:
 1. A wobble plate drive, comprising: a stator gear having acentral stator axis and a plurality of stator teeth disposed on an innercylindrical surface; a wobble plate having a wobble axis disposed at anon-zero wobble angle relative to the stator axis, an engaging faceperpendicular to the wobble axis, a plurality of face teeth disposed onthe engaging face, and a plurality of wobble teeth disposed around aperimeter of the wobble plate and configured to engage with the statorteeth; and a rotor plate substantially aligned with the stator axis andhaving a plurality of rotor teeth configured to engage with the faceteeth; wherein at least two of the pluralities of teeth are configuredto engage with each other in a self-aligning manner such that as thewobble plate nutates around the stator gear, the wobble angle remainsconstant without support from a fulcrum.
 2. The wobble plate drive ofclaim 1, wherein: at least one of the wobble teeth is wedge shaped, witha surface of the at least one wobble tooth defining a first lineextendable through a center of mass of the wobble plate; and at leastone of the stator teeth is wedge shaped, with a surface of the at leastone stator tooth defining a second line extendable through a center ofmass of the wobble plate.
 3. The wobble plate drive of claim 1, wherein:The face teeth are disposed on a frustoconical surface of the wobbleplate such that a center of mass of the wobble plate coincides with avertex of the frustoconical surface of the wobble plate; and the rotorteeth are disposed on a frustoconical surface of the rotor plate suchthat the center of mass of the wobble plate coincides with a vertex ofthe frustoconical surface of the rotor plate.
 4. The wobble plate driveof claim 1, wherein the wobble plate is constrained such that duringnutation no part of the wobble plate is more than a predetermineddistance from the stator gear.
 5. The wobble plate drive of claim 1,wherein the wobble teeth and the face teeth extend in oppositedirections parallel to the wobble axis, and the wobble plate is disposedbetween the stator gear and the rotor plate.
 6. The wobble plate driveof claim 1, wherein the wobble teeth and the face teeth extend in thesame direction parallel to the wobble axis, and the stator gear isdisposed between the wobble plate and the rotor plate.
 7. The wobbleplate drive of claim 6, further comprising a motor configured to inducenutation of the wobble plate about the stator gear, wherein nutation ofthe wobble plate about the stator gear causes the wobble plate torotate, and rotation of the wobble plate causes the rotor plate torotate.
 8. The wobble plate drive of claim 7, wherein: the motorincludes a permanent magnet and a set of electromagnetic coils; thewobble plate is made of a magnetically susceptible material; and thepermanent magnet and the set of electromagnetic coils are collectivelyconfigured to create a magnetic field between the motor and the wobbleplate with a moving point of highest flux density.
 9. A wobble platedrive, comprising: a stator gear having a central stator axis and aplurality of stator teeth disposed on an inner cylindrical surface; awobble plate having a wobble axis disposed at a non-zero wobble anglerelative to the stator axis, an engaging face perpendicular to thewobble axis, a plurality of face teeth disposed on the engaging face,and a plurality of wobble teeth disposed around a perimeter of thewobble plate in a plane perpendicular to both the engaging face and thewobble axis; and a rotor plate substantially aligned with the statoraxis and having a plurality of rotor teeth configured to engage with theface teeth; and means for self-aligning engagement of the stator teethwith the wobble teeth, such that the wobble angle remains constantwithout support from a fulcrum as the wobble plate nutates around thestator gear.
 10. The wobble plate drive of claim 9, wherein: at leastone of the wobble teeth is wedge shaped, with a surface of the at leastone wobble tooth defining a first line extendable through a center ofmass of the wobble plate; and at least one of the stator teeth is wedgeshaped, with a surface of the at least one stator tooth defining asecond line extendable through a center of mass of the wobble plate. 11.The wobble plate drive of claim 9, wherein: the face teeth are disposedon a frustoconical surface of the wobble plate such that a center ofmass of the wobble plate coincides with a vertex of the frustoconicalsurface of the wobble plate; and the rotor teeth are disposed on afrustoconical surface of the rotor plate such that the center of mass ofthe wobble plate coincides with a vertex of the frustoconical surface ofthe rotor plate.
 12. The wobble plate drive of claim 9, wherein thewobble plate is constrained such that during nutation no part of thewobble plate is more than a predetermined distance from the stator gear.13. The wobble plate drive of claim 9, wherein the wobble teeth and theface teeth extend in opposite directions parallel to the wobble axis,and the wobble plate is disposed between the stator gear and the rotorplate.
 14. The wobble plate drive of claim 9, wherein the wobble teethand the face teeth extend in the same direction parallel to the wobbleaxis, and the stator gear is disposed between the wobble plate and therotor plate.
 15. A method of operating a wobble plate drive, comprising:providing a stator gear, a wobble plate, and a rotor plate; engaging aplurality of stator teeth of the stator gear with a plurality of wobbleteeth of the wobble plate in a self-aligning manner; engaging aplurality of face teeth of the wobble plate with a plurality of rotorteeth of the rotor plate in a self-aligning manner; and inducingnutation of the wobble plate about the stator gear such that an anglebetween the wobble plate and the stator gear remains constant withoutsupport from a fulcrum.
 16. The method of claim 15, wherein inducingnutation of the wobble plate includes: energizing a motor to rotateabout a rotation axis, the motor having a substantially flat surface andat least one rounded protrusion extending from the substantially flatsurface; and engaging the at least one rounded protrusion with asubstantially flat surface of the wobble plate, thereby causing thewobble plate to nutate.
 17. The method of claim 15, wherein inducingnutation of the wobble plate includes: energizing a motor including apermanent magnet and a set of electromagnetic coils to create a magneticfield between the motor and the wobble plate with a highest flux densityat a mobile location, thereby causing the wobble plate to nutate. 18.The method of claim 15, wherein: inducing nutation of the wobble plateincludes rotating the rotor plate; rotating the rotor plate when theface teeth are engaged with the rotor teeth causes the wobble plate torotate; and rotation of the wobble plate when the stator teeth areengaged with the wobble teeth causes the wobble plate to nutate.
 19. Themethod of claim 15, further including constraining the wobble plate suchthat during nutation no part of the wobble plate is more than apredetermined distance from the stator gear.
 20. The wobble plate driveof claim 1, wherein the at least two of the pluralities of teeth areconfigured to engage with each other in a self-aligning manner such thatas the wobble plate nutates around the stator gear, the wobble angleremains constant without supportive contact between the wobble plate anda centrally disposed support structure.